Submersible pumping units in use heretofore have included a hydraulic motor driving an axial flow pump and both mounted in a casing that is lowered into a water-filled ditch, trench or excavation in the ground to pump the water up through a discharge pipe extending on the opposite side of the hydraulic motor from the axial flow pump. The hydraulic motor is connected through hoses or pipes to an above-ground pump, which pumps oil through the hydraulic motor to drive it, with the return flow of oil going back to an above-ground tank which supplies the oil to the above-ground pump.
The hydraulic and the pump in the submersible pumping unit are stopped by turning off the above-ground pump. When this happens, the water in the discharge pipe above the submersible pump unit tends to flow back down by gravity and rotate the impeller of the submerged pump in reverse. This pump, in turn, tends to drive the hydraulic motor in reverse, causing the latter to pump oil in reverse through the above-ground pump. An important aspect of the present invention relates to a novel check valve arrangement for preventing such reverse flow of oil through the hydraulic motor in the submersible pumping unit and from there through the above-ground pump.
Another aspect of this invention is directed to filtering out any damaging particles which ar pumped out of the oil tank toward the inlet of the above-ground pump.
Another aspect of this invention is concerned with relieving excessive pressure at the outlet side of the above-ground pump, such as during abnormal operating conditions or upon starting the prime mover for this pump.